The present invention pertains to novel thermosettable polymeric cyanates.
Thermosettable aromatic or bridged aromatic cyanates and the polytriazines resulting from curing of said cyanates are known in the prior art, for example, as taught by German Pat. Nos. 1,190,184; 1,195,764; and 1,720,740. In U.S. Pat. No. 3,694,410, a variety of polymeric dicyanates of the structure NC--O--R--O--CN with R being an oligomeric chain of bridged aromatic nuclei are taught. These dicyanates, however, suffer in reactivity upon curing due to the presence of the large bridging (R group) structures which inherently lower the density of curable cyanate groups. Further, the properties of these cured compositions become largely dependent upon said bridging (R group) structures rather than the polytriazine functionality, per se. As is emphasized in U.S. Pat. No. 4,094,852, the moisture sensitivity of the prior art polytriazines is unacceptably high.
A co-pending application by Robert E. Hefner, Jr. entitled "Poly(Cyanato)Poly(Alkenyl Phenol) Compositions" teaches the preparation and curing of novel poly(cyanato)poly(alkenyl phenol) compositions. Said compositions provide cured products with excellent overall properties, however, for the preparation of poly(cyanato)poly(alkenyl phenol)homopolymers, it would be desirable to reduce the number of cyanate groups within the poly(alkenyl phenol) chains without leaving free phenolic hydroxyl groups which are capable of decreasing moisture resistance.
The present invention provides polymeric cyanates of high reactivity and useful cured compositions via homopolymerization to the polytriazines. Polymeric cyanate compositions containing controlled numbers of cyanate groups within the polymer chains are obtained without the penalty of leaving unreacted free phenolic hydroxyl groups. Copolymerization of these polymeric cyanates with difunctional cyanates of the prior art provides polytriazines with improved mechanical properties and reduced moisture sensitivity. Copolymerization of these polymeric cyanates with epoxy resins provides useful cured compositions containing both triazine and oxazoline structures. These resins are useful in the preparation of laminates, castings, coatings and the like.